Caspase-1 activity is required to bypass macrophage apoptosis upon Salmonella infection

Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA.
Nature Chemical Biology (Impact Factor: 13). 07/2012; 8(9):745-7. DOI: 10.1038/nchembio.1023
Source: PubMed


Here we report AWP28, an activity-based probe that can be used to biochemically monitor caspase-1 activation in response to proinflammatory stimuli. Using AWP28, we show that apoptosis is triggered upon Salmonella enterica var. Typhimurium infection in primary mouse bone marrow macrophages lacking caspase-1. Furthermore, we report that upon Salmonella infection, inflammasome-mediated caspase-1 activity is required to bypass apoptosis in favor of proinflammatory pyroptotic cell death.

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Available from: Matthew Bogyo, Oct 04, 2015
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    • "A sublytic caspase-1 activity (activity observed in absence of cell death) has been previously described in epithelial cells (Gurcel et al., 2006) but it is still very poorly documented in primary macrophages. Due to the high level of cross-reactivity of the caspase-1 fluorescent probe FLICAcasp1 with other caspases activated in a caspase-1-independent manner (Pierini et al., 2012; Puri et al., 2012), we were unable to monitor caspase-1 activity at the single cell level. To investigate the presence of sublytic caspase-1 activity, we thus analyzed caspase-1 processing by western blot at 6 h PI (Figure 5E), i.e., before the detection of cell death (Figures 2A–C). "
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    ABSTRACT: The inflammasome is an innate immune signaling platform leading to caspase-1 activation, maturation of pro-inflammatory cytokines and cell death. Recognition of DNA within the host cytosol induces the formation of a large complex composed of the AIM2 receptor, the ASC adaptor and the caspase-1 effector. Francisella tularensis, the agent of tularemia, replicates within the host cytosol. The macrophage cytosolic surveillance system detects Francisella through the AIM2 inflammasome. Upon Francisella novicida infection, we observed a faster kinetics of AIM2 speck formation in ASC(KO) and Casp1(KO) as compared to WT macrophages. This observation was validated by a biochemical approach thus demonstrating for the first time the existence of a negative feedback loop controlled by ASC/caspase-1 that regulates AIM2 complex formation/stability. This regulatory mechanism acted before pyroptosis and required caspase-1 catalytic activity. Our data suggest that sublytic caspase-1 activity could delay the formation of stable AIM2 speck, an inflammasome complex associated with cell death.
    Frontiers in Cellular and Infection Microbiology 04/2013; 3:14. DOI:10.3389/fcimb.2013.00014 · 3.72 Impact Factor
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    • "The dependence of cell death in C34 cells on caspase-1 indicates they die by pyroptosis which is unaffected by Bcl-X L overexpression and does not involve ROS production and large decreases in ΔΨ m . Although pyroptosis does not involve the proteolytic maturation of caspase-3 (Puri et al, 2012) our results indicate it does have similarities to extrinsic 'type I' apoptosis (Galluzzi et al, 2012). This indicates that pyroptosis appears to occur without standard mitochondrial dysfunction pointing again to the evolution of a system designed to ensure cell death when pathogens employ strategies to affect mitochondrialassociated innate immune responses (Ashida et al, 2011). "
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    ABSTRACT: Infection of macrophages by bacterial pathogens can trigger Toll-like receptor (TLR) activation as well as Nod-like receptors (NLRs) leading to inflammasome formation and cell death dependent on caspase-1 (pyroptosis). Complicating the study of inflammasome activation is priming. Here, we develop a priming-free NLRC4 inflammasome activation system to address the necessity and role of priming in pyroptotic cell death and damage-associated molecular pattern (DAMP) release. We find pyroptosis is not dependent on priming and when priming is re-introduced pyroptosis is unaffected. Cells undergoing unprimed pyroptosis appear to be independent of mitochondrial involvement and do not produce inflammatory cytokines, nitrous oxide (NO), or reactive oxygen species (ROS). Nevertheless, they undergo an explosive cell death releasing a chemotactic isoform of the DAMP high mobility group protein box 1 (HMGB1). Importantly, priming through surface TLRs but not endosomal TLRs during pyroptosis leads to the release of a new TLR4-agonist cysteine redox isoform of HMGB1. These results show that pyroptosis is dominant to priming signals and indicates that metabolic changes triggered by priming can affect how cell death is perceived by the immune system.
    The EMBO Journal 12/2012; 32(1). DOI:10.1038/emboj.2012.328 · 10.43 Impact Factor
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